Numerous industries, including the automotive, industrial and aerospace industries, place stringent reliability requirements on their position sensing systems. Potentiometers are commonly known in the art for use in position sensing systems and are specifically used for determining displacement angles of motor controlled or regulated elements. Although potentiometers are a relatively inexpensive solution for position sensing, they are also susceptible to the effects of adverse environmental conditions and are subject to failure resulting from numerous operations over time. To overcome the disadvantages of potentiometer based sensing systems, non-contact sensors are increasingly being used to meet the stringent reliability requirements. Non-contact sensors are currently known in the art and may be based on various principles, including inductive, capacitive, Hall effect or magneto-resistive principles.
A non-contact sensor based on inductive principles in commonly known as an inductive position sensor, or a resolver. An inductive position sensor comprises a coil assembly having one or more excitation coils and two or more sensing coils. In the operation of an inductive position sensor, an alternating current (AC) is injected into the excitation coil(s) which results in the generation of a time varying magnetic field in the vicinity of the excitation coil. The time varying magnetic field is sufficient to induce a time varying voltage in the sensing coils as a result of the mutual magnetic coupling between the excitation coil and the sensing coils. To determine an angular position of a rotatable target with respect to the coil assembly, a conductive target is rotatably positioned within the time varying magnetic field between the excitation coil and the sensing coils. The presence of the rotatable target within the time varying magnetic field changes the mutual magnetic coupling between the excitation coil and the sensing coils, relative to the position of the rotatable target. The change in mutual coupling between the excitation coil and the sensing coils alters the time varying voltage induced in the sensing coils. Since the magnitude of the voltage change induced in the sensing coils is generally sinusoidal with respect to the angular position of the rotatable target relative to the coil assembly, the time varying voltage within the sensing coils can be measured and processed to determine the angular position of the rotatable target.
A coil assembly commonly used in conventional electromechanical resolvers is comprised of axial windings wound on a Ferro-magnetic core. However, this type of resolver assembly is expensive and consumes a considerable amount of space. In order to reduce the cost and size of resolvers, it is also known in the art to form planar coils on one or more printed circuit boards (PCB) to provide the coil assembly of the resolver. However, the design of planar coil assemblies for inductive sensors currently known in the art require that the coils be spread across multiple layers of the PCB and require a significant number of PCB vias between the PCB layers to establish the required connections between the layers. Utilizing multiple PCB layers and requiring numerous vias between the layers undesirably increases the cost of the inductive sensor assembly.
Accordingly, what is needed in the art is a non-contact angular position sensor utilizing a planar coil assembly that can be implemented on a printed circuit board (PCB) comprising a reduced number of PCB layers.